This invention relates generally to lenses, and more particularly relates to the measurement of a characteristic such as the focal length of a rod lens.
The precision of optical devices is directly related to the precision of the components used in the manufacture of such devices. For example, rod lenses, such as graded-index lenses are often used in the manufacture of optical devices and are often used within the devices themselves. These lenses are relatively inexpensive, compact, and useful as components in optical filters, and various other devices for coupling light from optical fibres, to components wherein a beam must be collimated. The typical configuration is a series arrangement of optical fibre, lens, component, lens, optical fibre, such that light exiting an optical fibre is collimated by the lens, the collimated beam propagates through the component, the collimated beam exiting the component is then focused, and is coupled back into an optical fibre. Hence there are instances when a lens of exactly a quarter pitch, i.e. a collimating lens is required, and, there are instances where graded-index lenses of other than a quarter pitch are required. For example some designs require a 0.23 pitch or a 0.26 pitch lens. The difficulty is that highly accurate methods of measuring the pitch or gradient of a graded-index lens are not commercially available. A method of measuring one or more lenses simply and at a reasonable cost, with precision of up to xc2x10.0002 for pitch and xc2x10.0002 mmxe2x88x921 for Root A would be desirable. Currently, suppliers of lenses profess to provide accuracy of xc2x10.0005 mmxe2x88x921 for Root A.
It is therefore an object of this invention to provide a system and method for measuring lens Root A with accuracy up to xc2x10.0002 mmxe2x88x921.
It is a further object of the invention to provide a measurement system that is relatively inexpensive to manufacture and easy to use that will provide a relatively high degree of accuracy for measuring focal length of a graded-index lens.
In accordance with this invention there is provided, a method of determining a characteristic of a graded-index lens comprising the steps of:
receiving light from two end faces of a graded-index lens within a distant light receiving/detection region;
locating a first focus spot from light received from one of the two end faces; locating a second focus spot from the other of the two end faces of the lens;
and determining a characteristic of the graded-index lens from a distance traversed to locate the two focus spots.
In accordance with another aspect of this invention there is provided, an optical system for measuring a characteristic of a lens related to its focal length or its gradient, comprising:
means for temporarily holding the lens during testing thereof;
a light source for irradiating the lens;
a beam splitter for directing light that has been received from the lens to an image plane;
means for relatively moving the lens and the image plane to vary a distance therebetween; and,
means for determining the varied distance.